What is obesity?

Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health.

Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person’s weight in kilograms divided by the square of his height in meters (kg/m2).

The WHO definition is:

A BMI greater than or equal to 25 is overweight

A BMI greater than or equal to 30 is obesity

BMI provides the most useful population-level measure of overweight and obesity as it is the same for both sexes and for all ages of adults. However, it should be considered a rough guide because it may not correspond to the same degree of fatness in different individuals.

Source: World Health Organisation Fact sheet N°311

Waist circumference is a less-common method used to measure obesity in an individual. This simple measurement indicates obesity and morbid obesity in adults by measuring your waist. To find your waist circumference, wrap a tape measure around the area above your hip bone and below your rib cage.

For females, a waist circumference of 89 centimetres or greater is considered unhealthy. For men, a waist circumference of 102 centimetres or greater is considered unhealthy. There is not a classification chart or various ranges used with this method to determine obesity. Only the simple thresholds for men and women noted above apply.

What causes obesity and overweight?

The fundamental cause of obesity and overweight is an energy imbalance between calories consumed and calories expended. Globally, there has been:

An increased intake of energy-dense foods that are high in fat; and

An increase in physical inactivity due to the increasingly sedentary nature of many forms of work, changing modes of transportation, and increasing urbanisation

Changes in dietary and physical activity patterns are often the result of environmental and societal changes associated with development and lack of supportive policies in sectors such as health, agriculture, transport, urban planning, environment, food processing, distribution, marketing and education.

Obesity is a disease often caused by factors largely beyond an individual’s control. Science shows that genetics play a role in obesity. Genes can cause certain disorders which result in obesity. However, not all individuals who are predisposed to obesity become obese. Research is currently underway to determine which genes contribute most to obesity.

Obesity is a chronic disease

Obesity facts infographic, click to download PDF

The WHO recognises that in this century, obesity has prevalence similar or higher than that of malnutrition and infectious diseases. For this reason, if drastic measures are not taken in order to prevent and treat obesity, more than 50% of the world population will be obese in 2025.

Obesity is, therefore, a chronic disease with enormous prevalence in developed countries, afflicting men and women of all races and ages.

Pre-obesity and obesity are important public health concerns demanding a joint strategy that includes the promotion of healthy eating habits and a more active lifestyle, as well as making available appropriate treatment and aftercare.

Childhood obesity

Particularly concerning is the growing incidence of childhood obesity in Europe.

Childhood obesity, particularly during the second decade of life, is now acknowledged to be an increasingly strong predictor of adult obesity, especially for extremely overweight children of obese parents.

There is also increasing evidence that obesity has damaging social, economic and health consequences. Hence, childhood obesity is now recognised as an important public health issue and this has been further heightened by the increasing prevalence of adult obesity in both developed and developing countries.